The invention process is concerned with the enhanced recovery of oil from underground formations. More particularly, the invention relates to a method for producing hydrocarbons with a combination drive and cyclic gas injection scheme to efficiently sweep the portion of a formation bounded by two vertical wells and a horizontal well.
Horizontal wells have been investigated and tested for oil recovery for quite some time. Although horizontal wells may in the future be proven economically successful to recover petroleum from many types of formations, at present, the use of horizontal wells is usually limited to formations containing highly viscous crude. It seems likely that horizontal wells will soon become a chief method of producing tar sand formations and other highly viscous oils which cannot be efficiently produced by conventional methods because of their high viscosity.
Various proposals have been set forth for petroleum recovery with horizontal well schemes. Most have involved steam injection or in situ combustion with horizontal wells serving as both injection wells and producing wells. Steam and combustion processes have been employed to heat viscous formations to lower the viscosity of the petroleum as well as to provide the driving force to push the hydrocarbons toward a well.
U.S. Pat. No. 4,283,088 illustrates the use of a system of radial horizontal wells, optionally in conjunction with an inverted 9 spot having an unusually large number of injection wells. U.S. Pat. No. 4,390,067 illustrates a scheme of using horizontal and vertical wells together to form a pentagonal shaped pattern which is labeled a "5 spot" in the patent, although the art recognizes a different pattern as constituting a 5 spot. Various combinations of vertical and horizontal wells are disclosed in U.S. Pat. Nos. 4,637,461; 4,645,003; 4,646,824; 4,662,441; 4,685,515, 4,702,314; 4,718,485 and 4,727,937.
U.S. Pat. No. 4,535,845 discloses a method for sweeping a portion of a formation with steam that is bounded by two vertical wells and a horizontal well. In this method, the vertical and horizontal wells are perforated throughout the hydrocarbon zone and steam is continuously injected through the first vertical well and the horizontal well. The process sweeps hydrocarbons through the formation and produces hydrocarbons only at the second vertical well.
A thermal fluid method of producing hydrocarbons bounded by two vertical wells and a horizontal well is disclosed in U.S. Pat. No. 4,682,652. In this invention, a thermal fluid is injected into the formation through the first vertical well. Hydrocarbons and other fluids are produced from the horizontal well located between the two vertical wells through a first perforated interval in the horizontal well located near the first vertical well. After depleting this area of the formation, the first perforated interval is closed off and the process is repeated for successively perforated intervals of the horizontal well, all of which are farther from the first vertical well than the preceding perforated intervals. Near the end of the process, production is taken through the second vertical well. An alternate embodiment discloses a cyclic injection, soak and production of thermal fluid through the horizontal well or the first vertical well prior to initiating the process.